Main

1046. Last Stone Weight/1046. Last Stone Weight.py

@@ -31,12 +31,8 @@ def lastStoneWeight(self, stones: List[int]) -> int:
         max_heap = [-val for val in stones]
         heapq.heapify(max_heap)
         while len(max_heap) > 1:
-            y = (-1) * heapq.heappop(max_heap)
-            x = (-1) * heapq.heappop(max_heap)
-            if x == y:
-                if not max_heap: # consider a case [1,1]
-                    return 0
-                continue
-            else:
-                heapq.heappush(max_heap,x-y)
-        return max_heap[0] if max_heap[0] > 0 else (-1)*max_heap[0]
+            stone1 = (-1) * heapq.heappop(max_heap)
+            stone2 = (-1) * heapq.heappop(max_heap)
+            if stone1 != stone2:
+                heapq.heappush(max_heap,-(stone1-stone2))
+        return -max_heap[0] if max_heap else 0

523. Continuous Subarray Sum/523. Continuous Subarray Sum.py

@@ -22,20 +22,12 @@
 """
 class Solution:
     def checkSubarraySum(self, nums: List[int], k: int) -> bool:
-        """
-        The idea here is if two sums have the same module and they are atleast two indexes apart then we can return true otherwise false.
-         For [0,2],  k=2 prefix sum would be [0,2] and sum2 = 2 and sum1 = 0. sum2 - sum1 can be divided by k and the distance between those two indexes is atleast 2.
-        """
-        hmap = {0:-1} # initially at index -1 the sum would be zero.
-        for i in range(1,len(nums)):
-            nums[i] += nums[i-1] # prefix sum
-        for i in range(len(nums)):
-            temp = nums[i]
-            if k:
-                temp %= k 
-            if temp in hmap.keys():
-                if i - hmap[temp] >= 2:
-                    return True
+        hmap,total = {},0
+        for i,num in enumerate(nums):
+            total = (total + num) % k
+            if total == 0 and i > 0: return True # if total % k =0 that means we have a multiple of k present already and check if the array size is greater than or equal to 2.
+            if total not in hmap:
+                hmap[total] = i
             else:
-                hmap[temp] = i
-        return False
+                if i - hmap[total] >= 2: return True
+        return False

988. Smallest String Starting From Leaf/988. Smallest String Starting From Leaf.py

@@ -0,0 +1,54 @@
+"""
+You are given the root of a binary tree where each node has a value in the range [0, 25] representing the letters 'a' to 'z'.
+
+Return the lexicographically smallest string that starts at a leaf of this tree and ends at the root.
+
+As a reminder, any shorter prefix of a string is lexicographically smaller.
+
+For example, "ab" is lexicographically smaller than "aba".
+A leaf of a node is a node that has no children.
+
+
+
+Example 1:
+
+
+Input: root = [0,1,2,3,4,3,4]
+Output: "dba"
+Example 2:
+
+
+Input: root = [25,1,3,1,3,0,2]
+Output: "adz"
+Example 3:
+
+
+Input: root = [2,2,1,null,1,0,null,0]
+Output: "abc"
+
+
+Constraints:
+
+The number of nodes in the tree is in the range [1, 8500].
+0 <= Node.val <= 25
+"""
+# Definition for a binary tree node.
+# class TreeNode:
+#     def __init__(self, val=0, left=None, right=None):
+#         self.val = val
+#         self.left = left
+#         self.right = right
+class Solution:
+    def smallestFromLeaf(self, root: Optional[TreeNode]) -> str:
+        q,result = collections.deque(),None
+        q.append((root,chr(root.val+97)))
+        while q:
+            node,path = q.popleft()
+            if not node.left and not node.right:
+                if not result:
+                    result = path
+                else:
+                    result = min(result,path)
+            if node.left: q.append((node.left,chr(node.left.val+97)+path))
+            if node.right: q.append((node.right,chr(node.right.val+97)+path))
+        return result